The occurrence, distribution, site fidelity, and school size of bottlenose dolphins (Tursiopstruncatus) in the coastal waters of north San Diego County, California were
assessed during a six-year boat-based photoidentification study. A total of 146
photographic surveys were conducted between January 1984 and December 1989. Dolphin
schools were encountered on 79% of all surveys, and 2869 individuals were observed in 145
separate schools. Three-hundred seventy-three dolphins were individually identified. All
schools were sighted within 1 km of shore, and more than two-thirds of the schools were
encountered in the southern half of the 32-km long study area. School size (mean = 19.8,
SD = 18.40) and the number of dolphins encountered per survey (mean = 26.8, S.D. = 22.3)
were highly variable. Low resighting rates of known individuals provided little evidence
for long-term site fidelity. When our six-year photoidentification database was combined
with previous data, 404 dolphins were identified in the study area from September 1981 to
December 1989. Jolly-Seber population estimates during the 1984-1989 study period varied
between 234 and 285. The combination of regular dolphin occurrence, low site fidelity by
known individuals, and the continuous increase in the rate at which new dolphins were
identified indicates that numerous different individuals were visiting the study area
across and within years. The open California coastline differs in habitat structure and
prey distribution from more protected study areas where bottlenose dolphins display site
fidelity. These habitat differences may help to explain the observed intraspecific
behavioral variability of this species.